Gonococcal and chlamydial infections continue to be major public health problems despite improved methods for diagnosis and the availability of effective therapy. As new methods for differentiation of gonococcal and chlamydial strains have become available, the correlation of different strains with differing clinical manifestations has become apparent. Gonococci of the AHU/IA-l and -2 auxotype/ serovar classes are associated with clinical manifestations which include disseminated gonococcal infection and asymptomatic urethritis in men, while other strains have been shown to be more common in homosexual men than in heterosexual men and women. Similarly, chlamydia of the Ll, L2 and L3 serovars tend to cause clinically more severe manifestations of disease (lymphogranuloma venereum, inflammatory proctitis) than the 12 serovars (A-K) of the trachoma biovar which are more often associated with clinically milder syndromes such as nongonococcal urethritis, cervicitis, pelvic inflammatory disease and epididymitis. Little is known however about the biologic factors which, affect the transmissibility of these pathogens. In this project the transmission of gonococcal and chlamydial infections in patients attending an inner city STD clinic and their partners will be comprehensively studied, comparing the relative transmissibility of different strains of each pathogen and the effect of prior infection on the risk of subsequent infection. In addition, data will be collected on numbers of exposures to sexual partners, contraceptive methods employed, and post-coital hygienic practices to control for the intensity of exposure to their partners' infection(s). Gonococci will be typed using auxotyping and monoclonal antibody serovar analysis and chlamydia will be typed using monoclonal antibodies in a dot-enzyme-linked immunosorbent assay (ELISA). In addition the impact of prior infection on susceptibility to infection will be measured using historical information and by determination of the presence of pre- existing anti-gonococcal and anti-chlamydial antibodies using immunoblot and microimmunofluorescence methods.